Sheep and cattle have been traditionally washed at abattoirs, prior to slaughter, by either hosing them down with a high pressure water hose, or by allowing the animals, particularly so in the case of sheep, to pass through a swim bath, in which the animals are almost totally immersed in water, and have to swim to the far side (usually with their head above water). Neither is satisfactory. A swim bath has the advantage that the movement of the animals though the bath tends to loosen some of the dirt, and may partially clean the animals. A swim wash used on its own may also provide a breeding ground for bacteria. The animal may superficially appear to be clean, but in fact may pick up bacteria from the bath, which may in turn contaminate the meat.
It is desirable to clean the pelt in such a way that it is not damaged, and it is also particularly desirable that dirt is removed from the pelt in at least those areas where incisions will be made by the slaughtermen, in order to minimise the risk of contamination of the meat either by cutting through a dirty pelt, or when the carcass is being opened up, a dirty portion of the pelt falling back on to the meat, giving rise to the possibility of contamination if dirt or bacteria from the pelt comes into contact with the open carcass.